Mulger bill wrote:New chain and used cassette? If you've still got the old chain, whip out the ruler and measure it...

New frame, so no old chain.

I have three wheelsets which get moved around between bikes (training/commuter bike - about to replace one chain as it hit 0.75%, race bike chain 3,0000km and still good and poseur bike - brand new chain 200km)Training wheelset, with 11-23 1070 cassette that has seen 3,000km on 3 different bikes/chains - no issuesRacing wheelset, with 11-23 OG 1090 cassette that has seen 1,500km on a single chain (race bike) this is what caused me grief on Thursday.Climbing wheelset with 11-26 1070 that has seen 500km on a single chain (race bike)

Have a lightly used chain from another project , I will try to see if that is an issue with the chain

in my experience skipping is nearly always a compatibility problem between the chain and cassette, assuming neither is worn. Once had really bad skipping with new components. Realised that I had put a mislabelled 8 spd chain on a 9 spd cassette.

old chain on new chainset could possibly cause slipping. i have had this problem several times and i always end up solving it with new drivetrain (chain, cassette, rings) across the board. one day i will learn